Excessive gestational weight gain (GWG), defined as GWG above the current Institute of Medicine (IOM) GWG guidelines is associated with adverse short and long-term health complications for women and their infants. Overweight and obese women are at already at high risk of complications due to their elevated weight, and excessive GWG further exacerbates their high risk of complications. Thus, there is an urgent need to help reduce excessive GWG in this high-risk population. Traditional high-intensity interventions to improve GWG among overweight and obese women have achieved success but are too time intensive for some women. In addition, studies show women consider behavior change advice to be more persuasive if it comes from their clinician, but clinicians have insufficient training on weight counseling. Thus, interventions aimed at reducing excess GWG among overweight and obese women that are practical for both women and clinicians are needed. Emerging evidence and our pilot work suggest that mobile health (mHealth) interventions for weight management can be effective in pregnancy, but a large-scale randomized trial in the real-world clinical setting is needed. We will conduct a cluster randomized controlled trial of 56 clinicians (caring for 2040 pregnant overweight/obese women) randomized to usual care or usual care plus an mHealth intervention. We propose an adaptive intervention that increases in intensity according to patients? GWG in relation to the IOM guidelines. Technology-based tools?including a mobile app, wireless ?smart? scale, wearable activity tracker, and diet tracking app?will enable convenient self-monitoring, feedback, and goal setting. These tools will provide largely automated, real-time feedback to patients via text messaging and will transmit real-time GWG, physical activity and diet data to a lifestyle coach and obstetric clinician. All patients of clinicians in the intervention, receive the technology-based tools, automated text messages and weekly e-mails of core lifestyle intervention sessions (Step 1). Step 2 is the addition of personalized text messages; and Step 3 is the addition of personalized 1:1 telephone coaching sessions, with these latter 2 Steps reserved for patients who need them. Clinicians in the intervention also receive training and tools embedded in the EHR to facilitate discussing GWG with their patients. Our primary aim is to evaluate whether an adaptive mHealth intervention designed to help overweight/obese women and their clinicians manage GWG will improve GWG in comparison to usual care. Our secondary aim will evaluate whether an mHealth intervention improves postpartum weight retention at 6 weeks, the proportion of infants with appropriate birthweight (<10th and >90th percentile) and infant growth trajectory from birth to 12 months. We will evaluate the cost-effectiveness of the mHealth intervention and possible adoption using a RE-AIM framework. If this mHealth intervention is proven effective, it could become a complementary part of clinical care, leading to better outcomes for mothers and their infants.